(a) Field of the Invention
The present invention relates to a mobile system and a moving method of the mobile system.
(b) Description of the Related Art
In general, an apparatus that moves using wheels as moving means, such as a vehicle or a robot, is driven under a no-slip condition to obtain an accurate correlation between the rotation of the wheels and the movement of the moving apparatus. In addition, driving torque should be guaranteed on a rough surface of a road, and the wheels on a floor surface should not generate friction noise when the moving apparatus is an indoor mobile apparatus.
Therefore, the wheels with an elastic material (e.g., rubber tire) can be used, for example, to move a mobile robot while satisfying the no slip condition, as shown in FIG. 1. In addition, a suspension system having a structure similar to an automobile suspension system may be additionally required when the mobile robot moves along a rugged terrain. In this instance, the mass of a main body of the mobile robot may be similar to that of a body mounted on a spring apparatus 202, as conceptually shown in FIG. 2.
As shown in FIG. 3, the mobile robot that is driven by rotation of the wheels has characteristics such that a central portion of the mobile robot tends to move opposite to a moving direction of the mobile robot when acceleration and deceleration are generated at a lower portion of the main body, such that the mobile robot receives a moment of inertia created by the inertia force. Herein, the moment of inertia is proportional to the height of the center of gravity. Therefore, as shown in FIG. 4, the mobile robot vibrates to and fro or left to right even though the mobile robot moves along flat ground within a fixed coordinate system.
In the case of a vehicle, similar to a mobile object moving by tractions of wheels, a squat phenomenon occurs during hard acceleration such that front portion (hood) of the vehicle is lifted and the rear portion (trunk) is pressed down, and a nose dive phenomenon occurs during hard deceleration such that the hood is pressed down and the trunk is lifted. The squat and nose dive phenomena are very important design criteria for performance and safety of the vehicle. In addition, the feel of the squat and nose dive are important sensitivity evaluation criteria for a user.
Visible vibration of a mobile robot affects performance and user satisfaction when determining quality of the mobile robot.
For example, design and construction of an intelligent mobile robot becomes user-oriented when the robot interacts with a standing person. Thus, images of the person are captured through an embedded camera, or the person's voice that is captured through an embedded microphone is played through an embedded-speaker.
Therefore, the height of the robot is relatively greater than a distance (wheelbase) between the axle of front wheels and the axle of rear wheels or a distance (track) between the axle of right wheels and the axle of left wheels. Accordingly, an effect of the inertial force on the robot is visualized into vibration in to and fro or left to right direction, unlike a vehicle.
Vibration of the robot occurs when driving the robot using a speed profile while ignoring the above-mentioned characteristics of the robot. In addition, various vibration modes may be activated at once according to a frequency component of a vibration activating force applied to the mobile robot. In this instance, a vibration mode activated by the lowest frequency has high visibility because of a long period and large amplitude, and thus it may have a bad influence on a user's sensitivity evaluation.
Therefore an existing speed profile, such as a speed profile or an acceleration profile for driving a motor, is used as a speed profile for the mobile robot. A given acceleration is performed during an acceleration/deceleration period according to a trapezoidal speed profile, which is the most commonly used speed profile. However, discontinuity of acceleration causes other vibration modes to be activated. In addition, when an S-speed profile is used, acceleration linearly increases from 0 and then linearly decreases such that an impulsive force is rarely generated therefrom. However, the S-speed profile may produce a transient response when the linear acceleration/deceleration of the S-speed profile is not properly considered.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.